FIG. 1 is an illustration of a cell 20 in a wireless communication system. As illustrated, the cell 20 has varying features, such as trees 26, hills 24 and buildings 281, 282. As wireless users move around the cell 20, the wireless channel conditions change as a result of these features, weather, proximity to the base station 22 and other factors.
Wireless systems typically have features to compensate for changes in channel conditions, such as transmission power control and automatic frequency control. These compensation techniques operate blindly in a reactive manner. To illustrate, a wireless user communicating with a base station 22 encounters a small fade in the received signal power, such as due to an obstruction. The base station 22 senses a drop in the measured signal to interference ratio (SIR) and instructs the user to increase its power level accordingly.
Such compensation features may not be sufficient in certain situations. If channel conditions change dramatically, such as a result of a deep fade or severe Doppler shift, the reactive compensation techniques may not keep pace and the link quality suffers, resulting is unacceptable quality of service (QOS). If the channel conditions change too rapidly, the communication links between the wireless user and the base station 22 may even be lost.
Accordingly, it is desirable to be aware of such wireless channel conditions.